Cryosurgery is a surgical procedure that uses freezing temperatures to destroy tissue. Its history began in 1865 when James Arnott, an English physician, used this method for the treatment of skin cancer. Modern applications of cryosurgery are numerous. For example, an early cryosurgical apparatus was developed by Dr. Irving Cooper, a New York surgeon, and used for treatment of Parkinson's disease. The apparatus includes an insulated tube or Cannula which has a cold-tip through which liquid nitrogen is circulated. A dime-sized hole is trepanned into the skull to allow for insertion of the cannula. Once the cannula is inserted, the cold-tip is manipulated to destroy a small amount of brain tissue (the thalamus) by freezing it. Starting with the apparatus of Cooper, many modifications for improvement of cryosurgery instruments have been proposed and developed into useful devices. These prior art devices have generally been of two types. One type uses a spray of cold gas and/or liquid applied directly to the tissue to be destroyed; the other uses a closed-end probe wherein a refrigerant is delivered to its distal end cold-tip, which is applied onto or inserted into the tissue to be destroyed. Applications of cryosurgery and the temperature-time histories used in such procedures vary from -60 to -5 degrees fahrenheit applied for 2 to 5 seconds for repair of a detached retina to near -320 degrees fahrenheit applied for several minutes for the destruction of cancerous tumors.
A review of the prior art is presented in U.S. Pat. No. 4,946,460. This patent also describes the current scientific understanding of the process of necrosis (tissue death) by freezing and its translation into the efficacy of programmed control of the temperature history of the target tissue during the freezing processes attendant to specific surgical procedures. In the above and descriptions to follow, the terms cryogenic, cryosurgery, cryogen, etc. are used to reference any temperature which is low with respect to common climatic temperatures. Although among those working in the field of cryogenics, it is common to regard the upper limit of the field to be in the neighborhood of -240 degrees fahrenheit, this temperature limit is purely one of choice since there is no single outstanding feature that clearly defines an upper bound.